1. Field of the Invention
This invention relates to an image forming-apparatus such as a copying machine and a printer which uses an electrophotographic process and particularly to transfer-controlling in the image forming apparatus.
2. Description of Related Art
The most basic function of the transfer unit in the image forming apparatus is to transfer toner images completely from an image bearing member to transfer paper or intermediate transfer member or to transfer primary transferred toner images from an intermediate transfer member completely to transfer paper as secondary images. Various transfer-bias controlling technologies have been proposed to effectively control the basic transfer function of the transfer unit.
For example, one of such technologies is the ATVC (Active Transfer Voltage Control) technology. The ATVC technology applies a current to the transfer unit while no image is formed, reads this current and voltage values, and determines an optimum transfer bias. (See Japanese Patent Application 2001-117376.)
Another proposed technology takes steps of forming a plurality of toner patches of the same shape on a photoreceptor, applying different intermediate transfer biases to the toner patches, intermediately transferring the toner patches to an intermediate transfer member, detecting the quantity of toner attached to each toner patch on the intermediate transfer member, and determining an optimum intermediate transfer bias. (See Japanese Patent Application 2000-321832.)
Still another proposed technology is a prospective control technology which selects a predetermined transfer bias according to the result of measurement of environmental conditions such as relative humidity in actual image formation processes and running times of the image forming apparatus.
However, in every conventional technology, it has been difficult to prevent transfer failures due to immigration of great particles in toners.